Plasma guns take aim at larger surfaces.

Plasma guns take aim a larger surfaces

New technologies for tailoring the surfaces of materials for specific purposes are making engineers' dreams come true. Ion implantation, for instance, allows manufacturers to embed atoms of another material into silicon semiconductors and to produce tougher ball bearings by adding a stronger metal to their surfaces. For the most part, however, this exciting technique has proved too expensive and cumbersome for items much bigger than a computer chip or a ball bearing.

Now, three researchers have developed a way to implant metal ions (charged atoms) or to lay down a thin metallic film with less fuss. In the April 1 APPLIED PHYSICS LETTERS, plasma physicist Ian G. Brown and his colleagues at the Lawrence Berkeley (Calif.) Laboratory report using a vacuum-arc plasma gun to generate a dense fog of metal ions in a vacuum chamber. The researchers then create a high voltage, or electric-potential differences, in the vacuum. This drives the metal into the surface of the material they wish to modify.

"This technique is scalable up to a very, very large throughput," Brown told SCIENCE NEWS.

Though researchers can generate plasmas in many ways, Brown says the pulsed vacuum-arc process he uses is more straightforward. This longstanding technique, which Brown considers underused, vaporizes atoms directly into ions by applying pulses of intense electric current to a metal plate. "Plasma guns are simple, cheap and efficient," Brown adds.

Some surface-modifying technologies, such as physical vapor deposition, also lay down wear-resistant films, but in much thicker layers. Techniques such as sputtering lay down thinner layers, but are "very expensive and limited to not very large components," notes John Stringer, a technical director at the Electric Power Research Institute in Palo Alto, Calif.

Brown can not only vary the thickness of the film he lays down, but also implant several metals simultaneously. By raising or lowering the voltage of the bursts that pull the ions toward the surface, he can control whether the metal plasma forms a thin film or instead penetrates to a certain depth. And by shooting plasma guns that generate different metal fogs, he can mix and match the materials being implanted.

In the new experiments, the researchars first added yttrium to silicon, shoving 65 quadrillion atoms onto every square inch of silicon. Then they used two plasma guns, one loaded with yttrium and the other with titanium, to build up alternating layers of the two materials. Next they plan to scale up the technology, using an array of six or more plasma guns to modify a 4-inch long, 4-inch-diameter pipe.

"There's nothing technically holding it back from becoming viable," engineer Bruce C. Haywood of Spire Corp. in Bedford, Mass., told SCIENCE NEWS. "But it takes money and time to commercialize it." About half of his company's business involves ion implantation, primarily of ball bearings and biomedical devices.